1. Field of the Invention
The present invention relates to a method of storing data, which is to be implemented in a radar, used for a vehicle, that has the function of detecting the presence of a plurality of target objects located in front of a moving vehicle (driver's own vehicle), on the basis of a plurality of detected data obtained by detecting signals reflected from the plurality of target objects. In this case, the plurality of detected data is temporarily stored in a data buffer or the like for the purpose of assuredly verifying whether or not the plurality of target objects are actually present, so as to thus prevent erroneous detection of noise or the like as data representing one of these target objects.
2. Description of the Related Art
In general, a radar used for a vehicle is disposed in a moving vehicle in order to detect a plurality of target objects (or a single target object) including an obstacle located in front of the moving vehicle and another vehicle or the like, which the moving vehicle is following, according to an adaptive cruise control (ACC) method. The radar used for the vehicle, such as a frequency-modulated continuous-wave (FM-CW) radar, detects the presence of a plurality of target objects located in front of the moving vehicle by utilizing a modulated signal, such as a frequency-modulated wave.
This type of FM-CW radar transmits the modulated signal, such as the frequency-modulated wave, to the plurality of target objects located in front of the moving vehicle, and detects signals reflected from the plurality of target objects so as to obtain a plurality of detected data. Based on the plurality of detected data, the FM-CW radar calculates the distances between the moving vehicle and the plurality of target objects and the relative speeds of the moving vehicle relative to the target objects. Thus, the FM-CW radar has the function of detecting the presence of the plurality of target objects. Details of the configuration of the FM-CW radar will be described later in “DESCRIPTION OF THE PREFERRED EMBODIMENTS”.
In particular, in the radar used for the vehicle, such as the FM-CW radar, if a plurality of target objects including an obstacle located in front of a moving vehicle and another vehicle or the like, which the moving vehicle is following, are present, the presence of the plurality of target objects must be detected accurately. For this purpose, it must be verified whether or not a plurality of detected data obtained by detecting signals reflected from the respective target objects has continuity, or it must be verified whether or not the target objects are actually present. A central processing unit (usually abbreviated to “CPU”) included in a microcomputer is operated in order to accurately and rapidly carry out the verification mentioned above. Consequently, the plurality of detected data and data relevant to the respective detected data must be temporarily stored in a memory unit, such as a data buffer, included in the microcomputer. However, the storage capacity of the data buffer included in the microcomputer has a maximum capacity. The larger the quantity of data stored in the data buffer becomes, the longer the operating time necessary to deal with the data becomes. From this viewpoint, the storage capacity of the data buffer that can be prepared for the above-mentioned verification is restricted to a limited amount.
In a conventional method of storing detected data or the like, when the detected data or the like is stored in the data buffer included in the microcomputer incorporated in the radar used for the vehicle, such as the FM-CW radar, the highest priority is assigned to the detected data that is being continuously detected (that is, the detected data that is judged to have continuity with high possibility). Data that is newly detected is stored in the data buffer only when the data buffer has an empty area. When an existing target object recedes from the moving vehicle or passes ahead the moving vehicle, the target object is not detected any longer. In this case, detected data stored in the data buffer is cancelled in order to obtain an empty area in the data buffer (please refer to, typically, Japanese Unexamined Patent Publication (Kokai) Nos. 9-80149 and 10-206532).
However, according to the foregoing conventional method, if numerous target objects are present around a moving vehicle, the data buffer included in the microcomputer has no empty area. It takes much time, relatively, to verify whether or not the newly detected numerous target objects are actually present and to accurately detect the presence of the target objects. This results in the delay in the detection of the target objects that is currently necessary for smoothly traveling the moving vehicle. Consequently, the time delay in detecting the target objects causes a delay in controlling the moving vehicle utilizing a conventional ACC (Adaptive Cruise Control) system.